The National Union of Workers says strike action at a Coles distribution warehouse in Melbourne's north could disrupt the supply of products to supermarket shelves.

About 600 employees at a major distribution warehouse at Somerton stopped work this morning.

The workers have set up a picket line and have stopped trucks from entering or leaving the building in protest at the outsourcing of their warehouse.

As Toll's trucks tried to enter the facility this morning, workers stood in front of them chanting: "No-one in, no-one out".

In one case, a truck kept edging forward, nudging a worker in the stomach, before driving away. A short time later some of Toll's HR team managed to force their way through the picket line, angering the protesters.

NUW state secretary Tim Kennedy says the workers are managed by contractor Toll Holdings and do not receive the same conditions as staff at other Coles warehouses across the country.

He says the action could disrupt the supply of products to supermarket shelves.

"These are fundamental pieces of distribution facilities, to make sure that when people go to a Coles supermarket, the type of product they want to buy, its reliability is there on the shelf," he said.

"If this warehouse is not working, that reliability will probably be impaired pretty quickly. And people will probably make the decision not to take the risk on whether their preferred brand of biscuit is there or not and probably go to the competitor."

Other Toll sites and other Coles sites get more than we get, and we're just asking for a fair go.

Worker at Somerton distribution warehouse

Workers told the ABC they want the same conditions offered to other Coles warehouses across the country.

"The company promised us three years ago, on its EBA, RDOs and shift loadings. It didn't come through," one worker said.

"Other Toll sites and other Coles sites get more than we get, and we're just asking for a fair go," another said.

A third worker told the ABC: "Toll are a subsidiary of Coles and so they're paying us, but everything in there is Coles. So why can't Coles pay us directly like other warehouses?"

Mr Kennedy said the workers were forced to take the strike action after Toll Holdings refused to budge on negotiations.

"Our members believe that if a Coles shift worker in a Coles warehouse gets paid a shift loading for working an afternoon shift or a night shift, then Toll shift workers doing exactly the same work in a Coles warehouse supplying Coles supermarkets should also be paid a shift loading for performing shiftwork," he said in a media release.

Mr Kennedy called for Coles to provide standard conditions for workers.

"The workers have voted overwhelmingly to take this strike action as they are sick of Coles ignoring their rights. They believe all workers should be treated equally," he said.

"Ultimately this is a Coles decision. They need to acknowledge their responsibility in creating a solution to the unequal treatment of workers in their warehouses."

'Contingency arrangements'

Toll spokesman Christopher Whitefield told the ABC that the current agreement at Somerton pays around 30 per cent above the award.

"It is important to note that contrary to NUW claims, of the more than 600 employees working at Somerton, less than half endorsed the taking of indefinite industrial action," he said.

He says that the company is offering the equivalent of a 4 per cent pay increase.

"The conditions negotiated at this site have enabled us to attract and retain the same high calibre workers that Toll employs around the country."

A spokesman for Coles says the EBA discussions at Somerton are matters for the NUW and Toll to resolve.

"Coles hopes that the discussions can be resolved swiftly but has put contingency arrangements in place to ensure minimal disruption to our Victorian customers," he said.

"As EBA agreements are negotiated on a site-by-site basis it is not appropriate to compare terms and conditions across sites. That's just like comparing oranges and apples."

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